Wanqin Zhou

Design and fabrication of heterojunction photocatalysts for energy conversion and pollutant degradation

Photocatalysis has attracted much attention for its promise in converting solar energy to chemical energy and in degrading various pollutants. Many recent investigations have demonstrated photocatalysts with well-defined junctions between two semiconductors with matched electronic band structures. Such structures effectively facilitate charge transfer and suppress recombination of photogenerated electrons and holes, leading to extremely high activity and stability. In this review, we focus on the influence of the heterojunction on the performance of semiconductor photocatalysts, including TiO2-based, ZnO-based, and Ag-based semiconductor photocatalysts. We also investigate fabrication methods for heterojunctions and attempt to understand the mechanisms behind photocatalysis. Finally, we propose challenges to design and clarify the mechanism for enhancing the effect of the heterojunction on photocatalyst performance.

Ultrasonic fabrication of N-doped TiO2 nanocrystals with mesoporous structure and enhanced visible light photocatalytic activity

An ultrasonic method was developed to fabricate novel mesoporous TiO2 nanocrystals doped with a high concentration of N (N/TiO2). The nanocrystals were characterized by physicochemical methods including N2 physical adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic degradation of dimethyl phthalate, a hazardous chemical in water, by the prepared N/TiO2 nanocrystals under visible light irradiation (400–660 nm) was investigated. The results show that N-doping efficiency under ultrasonic irradiation is 3.2 times higher than under typical conditions, and the produced TiO2 nanocrystals have mesoporous structure. N/TiO2 fabricated under ultrasound exhibited much higher efficiency for the degradation of dimethyl phthalate than that prepared under typical conditions. The high photocatalytic degradation activity of N/TiO2 fabricated under ultrasound is mainly attributed to its high N content effectively increasing its ability to absorb visible light.

Sonochemical fabrication, characterization and enhanced photocatalytic performance of Ag2S/Ag2WO4 composite microrods

Abstract Ag 2 S/Ag 2 WO 4 composite microrods, with lengths of 0.2–1 µm and diameters of 20–30 nm, were fabricated by a facile sonochemical route. The as-synthesized products were intensively investigated by a series of physicochemical characterizations, such as N 2 physical adsorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, diffuser reflectance spectroscopy, X ray photoelectron spectroscopy, photoluminescence spectroscopy and photocurrent response measurements. Ultrasonic irradiation yields an obvious improvement in the photocatalyst texture, for example, an increase in crystallinity and surface area. Moreover, sonochemically fabricated Ag 2 S/Ag 2 WO 4 microrods display strong visible light absorption and a high transient photocurrent response. The produced intimate Ag 2 S/Ag 2 WO 4 interface between Ag 2 S and Ag 2 WO 4 crystal phases largely promotes the separation of photogenerated holes and electrons. High photocatalytic activity and stability were obtained over Ag 2 S/Ag 2 WO 4 composite microrods. The dye degradation rate constant of Ag 2 S/Ag 2 WO 4 was 4.7 times and 29.8 times higher than that of bare Ag 2 WO 4 and Ag 2 S, respectively.

Novel Ni/CeO2-Al2O3 composite catalysts synthesized by one-step citric acid complex and their performance in catalytic partial oxidation of methane

Abstract A series of novel Ni/CeO 2 -Al 2 O 3 composite catalysts were synthesized by one-step citric acid complex method. The as-synthesized catalysts were characterized by N 2 physical adsorption/desorption, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, hydrogen temperature-programmed reduction (H 2 -TPR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry analysis (TGA). The effects of nickel content, calcination and reaction temperatures, gas hourly space velocity (GHSV) and inert gas dilution of N 2 on their performance of catalytic partial oxidation of methane (CPOM) were investigated. Catalytic activity test results show that the highest methane conversion (>85%), the best selectivities to carbon monoxide (>87%) and to hydrogen (>95%), the excellent stability and perfect H 2 /CO ratio (2.0) can be obtained over Ni/CeO 2 -Al 2 O 3 with 8 wt% Ni content calcined at 700 °C under the reaction condition of 750 °C, CH 4 /O 2 ratio of 2 : 1 and gas hourly space velocity of 12000 mL·h −1 ·g −1 . Characterization results show that the good catalytic performance of this composite catalyst can be contributed to its large specific surface area (∼108 m 2 ·g −1 ), small crystallite size, easy reducibility and low coking rate.

Preparation, characterization and photocatalytic performance of heterostructured AgCl/Bi2WO6 microspheres

Bi2WO6 microspheres with a diameter of 1.5–2 μm were prepared by a hydrothermal method, and then coated with different contents of AgCl to form heterostructured AgCl/Bi2WO6 microspheres. The prepared Bi2WO6 and AgCl/Bi2WO6 photocatalysts were characterized by X-ray diffraction, N2 physical adsorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activity of the catalysts was evaluated by photocatalytic degradation of rhodamine B under ultraviolet and visible light irradiation. Results showed that the deposition of AgCl had no obvious effect on the light absorption and surface properties of Bi2WO6. However, the heterostructured AgCl/Bi2WO6 photocatalysts exhibited considerably higher activity than the pure AgCl and Bi2WO6 catalysts. With the optimal AgCl content of 20 wt%, the photocatalytic activity of the heterostructured AgCl/Bi2WO6 catalyst was increased under both ultraviolet and visible light compared with that of Bi2WO6. The main reason for the enhanced photocatalytic activity is attributed to the formation of AgCl/Bi2WO6 heterostructures effectively suppressing the recombination of photogenerated electrons and holes.

Preparation and Characterization of GO/Ag 3 PO 4 Composite Photocatalyst and Its Visible Light Photocatalytic Performance

以石墨粉为原料,采用Hummers氧化法合成氧化石墨烯（GO）.然后在超声作用下,将不同含量的Ag3PO4沉积在GO上,制备了一系列4%（w,质量分数）GO/Ag3PO4、8%GO/Ag3PO4、16%GO/Ag3PO4和32%GO/Ag3PO4复合光催化剂.对所制备的光催化剂运用N2物理吸附、X射线粉末衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、拉曼光谱、傅里叶变换红外（FT-IR）光谱、紫外-可见漫反射吸收光谱（UV-Vis DRS）等手段进行了表征,并在可见光下考察了GO含量对Ag3PO4光催化降解甲基橙（MO）的性能.结果表明,GO能够和Ag3PO4实现均匀复合.复合GO提高了催化剂的比表面积,改善了催化剂的吸附性能.复合16%GO使Ag3PO4光催化活性提高最显著,120 min内对MO的降解率达到83%,是纯Ag3PO4光催化活性的7.5倍.GO能提高催化剂的比表面积,促进光生电子-空穴（e–/h＋）的分离,产生更多活性自由基,从而提高Ag3PO4光催化的活性和稳定性.